* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
a {
  text-decoration: none;
  color: #000;
}
li {
  list-style: none;
}
body {
  background: #f2f2f2;
}
.menu {
  position: fixed;
  width: 220px;
  height: 100vh;
  top: 0;
  left: 0;
  background: #23262e;
}
.menu .logo h1 {
  font-size: 18px;
  text-align: center;
  height: 50px;
  line-height: 50px;
  border-bottom: 1px solid rgba(0, 0, 0, 0.2);
}
.menu .logo h1 a {
  color: #fff;
}
.menu ul {
  margin-top: 20px;
}
.menu ul .menu_item {
  position: relative;
  text-indent: 2em;
  cursor: pointer;
  color: #fff;
  min-height: 50px;
  line-height: 50px;
}
.menu ul .menu_item span {
  margin-right: 5px;
}
.menu ul .menu_item .ico {
  position: absolute;
  top: 0;
  right: 15px;
  font-size: 12px;
}
.menu ul .menu_item .menu_down {
  display: none;
}
.menu ul .menu_item .menu_down .menu_down_item {
  background: #282b33;
}
.menu ul .menu_item .menu_down .menu_down_item a {
  margin-left: -15px;
  display: inline-block;
  width: 80%;
  height: 100%;
  color: rgba(255, 255, 255, 0.7);
}
main {
  width: 100%;
  padding-left: 220px;
}
header {
  height: 50px;
  background: #fff;
  box-shadow: 0px 0px 3px rgba(0, 0, 0, 0.2);
}
header .header_menu {
  float: left;
  margin-left: 20px;
  font-size: 2em;
  color: #444;
  line-height: 50px;
}
header .user {
  position: relative;
  float: right;
  margin-right: 50px;
  line-height: 50px;
  color: #444;
}
header .user span {
  font-size: 14px;
  color: #444;
}
header .user .user_down {
  top: 50px;
  left: -20px;
  width: 80px;
  text-align: center;
  background: #fff;
  position: absolute;
  opacity: 0;
}
header .user .user_down .user_down_item {
  transition: background;
  font-size: 14px;
}
@keyframes user_down {
  0% {
    opacity: 0;
    transform: translate(0, 20px);
  }
  100% {
    opacity: 1;
    transform: translate(0, 0px);
  }
}
header .user .user_down .user_down_item:hover {
  background: rgba(0, 0, 0, 0.2);
}
header .user:hover > .user_down {
  animation: user_down 0.3s;
  animation-fill-mode: forwards;
  opacity: 1;
}
